Advice please on restoring original Advents

[JKent]

Just bought my first pair of Advents--originals with the 10" Masonite-ring woofers. Any tips would be appreciated. Although I have refoamed AR and Allison speakers, these are new to me.

Pete B has been generous with his advice but I know he's pretty busy now and I have LOTS of questions, so I'm posting them here.

I know some people don't use shims, but my usual supplier, M-Sound, gives good arguments FOR shims. OTOH Pete, who has worked on Advents, writes "the LA woofer has to play up into the lower midrange and the dust cap is critical" so "don't cut the dust cap - these have lots of clearance easy to do by feel or with a test tone". That makes sense, too.

Pete also recommends "very high compliance foam". I asked M_Sound about that and got this reply:

The new foams have a larger roll, which look fairly large... although when measured (from the rear), are only 5/8" across but are fairly deep (which was what our main complaint about the old foam was). In any case, IF you glue them to the back of the fiber spacer, I hear they tend to look "right."

Any comments?

Pete also suggested "you might want to replace the inductors with air core." Do the Jantzen 20 ga inductors from Parts Express look like a good choice?

http://www.parts-express.com/mfg/jantzen/jantzen.cfm#15gauge

Also, M_Sound tells me " I am offering now that is great for these old classic speakers, is bypass caps for your tweeters' crossover capacitors. I offer them at an extremely attractive price; TWO for $2.00! They're metallized polypropylene 0.10uF 400V; perfect for bypassing your Tweeters' crossover caps."

Ideas concerning bypass caps?

Finally, in an earlier thread Pete wrote "Put a .47 ohm 5W resistor in series with the new caps to approximate the ESR of the original electrolytics". Would that be on BOTH the woofer and tweeter? I'll probably use some Dayton polys I have on hand.

thanks

Kent

[Pete B]

I use Aleen's tacky glue. I called their tech department before

trying it. They said it is just another PVA glue with slightly different

qualities as compared to Elmers:

http://www.save-on-crafts.com/alortacglu.html

I wrote this at another forum about refoaming the Advent/Dahlquist woofer:

You can use the free PC function generator software here:

http://duncan.rutgers.edu/physicsfreewares.htm

Try it on your PC speakers, set it to 500 Hz sinewave, not too loud.

Then set it to 20 Hz, hooked up to a hifi amp, and drive the woofer

that you're refoaming, start with the volume low and bring it up until

the cone moves about .1 - .25", let it center itself and listen for buzz or

scrape. Give it 30 seconds or so to center, then press the masonite

joint so that it sets tight when you're sure there's no scrape.

What I do is first glue to the cone, edge curve facing in of course with

the masonite woofers. Center this by eye, it's really not very difficult.

Let it fully dry, pressing a few times as it sets to keep it tight.

Then glue to the backside of the masonite, this also usually aligns,

simply by having the edge of the foam lined up with the cutout in the

masonite. These are wide clearance woofers which makes them much

more forgiving. A simple way is the gentle push test; push evenly with

thumb and fingertips spread evenly around the cone, you should not

hear or feel a scrape. Some people then push on one side only and a

slight scrape is OK, then try the opposite side only, should also have

slight or no scrape, then go 90 degrees and across again. Ususally,

there will be a slight scrape when pushing unevenly, as long as it's

about equal you should be fine. Again, press the glue joint a few times

as it sets to be sure that it is a tight joint. You can put a bit more glue

on the back of the masonite where it meets the edge of the foam to be

sure that it is air tight, just don't get it on the part of the foam that moves.

Some woofers do not tolerate the push test well because they have tight

clearances and fragile (wound on paper) voice coils, so it's not for all woofers.

The Advent certainly has no problem with this.

I hear that refoaming without removing the dust cap has been discussed in

detail at AK.

Consider this - one could glue the foam any which way with shims in place and

it would seem fine until you pulled out the shims. Shims are important when

doing the spider more so than the edge.

[Pete B]

If I was rebuilding a pair of OLAs for use as my main system without a

total crossover redesign or the goal for a completely original restoration,

I would do the following:

Check the woofer spider glue joints and repair with high temp epoxy.

Replace foam damping if used with fiberglass.

Replace the thin crossover board with either something like this:

http://meniscusaudio.com//tdcup-p-216.html

Or a .75" thick MDF replacement fully across the back to act also as an

additional brace. A few additional shelf braces would also help.

Replace both caps with low cost polys plus .47R ESR resistor:

http://www.classicspeakerpages.net/IP.Boar...790&hl=axon

These are a reasonable price and 3% tolerance:

http://meniscusaudio.com//-c-101_104.html

You want to roughly match the DCR of the inductors - this is how you would

select the gauge:

http://baselaudiolabs.googlepages.com/ADVENT_LA_XO.html

The large woofer inductor is ~1.6 mH .28R, so a 14 ga is about right, a bit

expensive though:

http://www.parts-express.com/pe/pshowdetl....tnumber=266-360

I'd replace the resistor with an Eagle.

I would rebuild it into the 16/8/3 version of the XO and the tweeter parallel

inductor can be a much smaller ga air core.

I would elminate the decrease position and perhaps make it an extended position

with a 4 uF cap.

I'd consider filling the area between the grille frame and baffle with foam or poly

damping material.

[JKent]

Thanks once again for all the info Pete.

Please bear in mind that my background and training are not in engineering, so there are some things I don't understand.

First--I don't find in the link how to match the DCR of the inductors. but those 14 ga ones do seem terribly expensive. I think if I can't use the lighter ga such as 18 I may just leave the originals.

I want to keep these as "stock" as possible, so rather than use a redesigned xo I'm inclined to replace what's there with film caps and Eagle or Mills resistors.

The M-Sound kits come with glue, so I won't need the Alene's (although I have a bottle on hand). Do the M-Sound foams seem right?

What do you think about the "bypass caps"?

Thanks again

Kent

[Pete B]

Thanks once again for all the info Pete.

Please bear in mind that my background and training are not in engineering, so there are some things I don't understand.

First--I don't find in the link how to match the DCR of the inductors. but those 14 ga ones do seem terribly expensive. I think if I can't use the lighter ga such as 18 I may just leave the originals.

I want to keep these as "stock" as possible, so rather than use a redesigned xo I'm inclined to replace what's there with film caps and Eagle or Mills resistors.

The M-Sound kits come with glue, so I won't need the Alene's (although I have a bottle on hand). Do the M-Sound foams seem right?

What do you think about the "bypass caps"?

Thanks again

Kent

OK, I had the impression that you were looking for improvements.

Look up and determine which crossover you have or want to copy, then read off the DCR of each

inductor from the parts list. Look for an air core with the same inductance and go up or down in

gauge to match the original DCR. Sure, film caps and new resistors are fine. I would not bother

changing the decrease inductor as I see no use for that position in the OLA.

I don't know the M-Sound kits, the only way to know is to measure the driver Fs after refoaming.

I have found some foam from others to be a bit stiff. Alene's has just the right set time for me.

I don't use bypass caps in speaker crossovers.

I would do all your work, leave the original inductors, then listen. Listen with BSC, and if you

decide to keep them you might want to reconsider the air core inductors. Hidley here was VP of

NHT speakers: http://www.diyaudio.com/forums/showthread....360#post1589360

[JKent]

Got 'em today and they appear in good shape. The seller said the SNs were missing but I found one INSIDE the spkr cab. It is A2-84386

Gluing to the BACK of the masonite ring looks like a real PITA compared to the refoam jobs I've done on AR speakers. Guess it will just take patience & care. I may try the rssound surrounds you recommend.

Several questions. I want to do an "original" restoration but if there are factory-sanctioned improvements OR changes that can easily be reversed I'd want to do that. So:

1. I do have the foam damping. If I replace with fiberglass, how much should I use?
   
2. It looks like the xo is rev 2. I have some Carli film caps on hand: 15uF and 8 uF. I'm assuming 15 is close enough but if I put in a PE order I'll get a couple of 16s.
   
3. Will replace the 3 ohm 5w resistors with Eagle or Mills
   
4. I'll consider filling the area between the grille frame and baffle with foam or poly damping material as you suggested.
   

I pried one xo (just the components) off and should be able to replace the caps and resistor, then glue the whole mess back to the masonite plate, but I'm looking at those inductors.

Pete, your reverse engineered rev 2 shows the following inductor values:

0.065mH 0.30 ohm

0.45mH 0.25 ohm

1.6mH 0.28 ohm

The closest I could find on PE was:

0.05mH 0.09 ohm (18 ga)

0.47mH 0.20 ohm (15 ga) OR 0.44mH 0.31 ohm (18 ga)

1.5mH 0.38 ohm (15 ga) OR 1.5mH o.28 ohm (14 ga)

You wrote that in "the 16/8/3 [rev 2] version of the XO ... the tweeter parallel inductor can be a much smaller ga air core."

The tweeter inductor is the "button", right? What exactly would you use? And as you pointed out, the inductors can be pricey. Looks like about $70 worth of inductors IF I use the ones noted from PE

You also wrote "I would not bother changing the decrease inductor as I see no use for that position in the OLA". Is that the 0.47mH? And is it the smaller iron-core one?

thanks again Pete (and anyone else who want's to contribute)

Kent

[Pete B]

1. As I recall the standard pink stuff fits the width just about right, run it top to bottom,

and put in enough uncompressed layers so that it is about 1" back from the baffle. Two

or 3 layers, I don't remember exactly.

2. Yes, either of those are fine.

3. Yes fine.

4. I've not tried it myself but there is a cavity there that the woofer drives into, perhaps

it was deliberate - I don't know. Worth trying an experiment.

I thought you were looking to upgrade - since you just want them stock, leave in the

original inductors if you prefer. The button is the smallest one, the small bar is the .45 mH,

and the large obviously is the 1.6 mH. The .44 mH 18 ga would be fine, and you can find

inductors at better prices on the net. He is out of many of the 14 ga air cores but has some

of the others:

http://www.zalytron.com/

[Pete B]

Gluing to the BACK of the masonite ring looks like a real PITA compared to the refoam jobs I've done on AR speakers. Guess it will just take patience & care. I may try the rssound surrounds you recommend.

Kent

I have a feeling Kent, that you're going to like these, especially if you try the BSC circuit.

The woofer is one of the best features of the LA. The masonite type is a bit of a pain to

work on, but it will be worth it. Rebuild it as original, take your time, and trust me you

will be impressed. Kloss got the woofer right, especially the large signal performance, it

is a remarkable driver in this regard.

Check that the masonite ring is mounted tight and air tight near the screw holes.

I do my best to get the old glue off. I've found that a Dremel tool, set to a slow speed

with the very small, soft wire brush works well to remove the glue from the cone - go

gently with it of course.

I put the driver face down on a bench and get the old glue on the masonite from behind

with a scraper such as a screw driver.

Align the cone to the new edge by eye. Also align the outer edge to the masonite by eye.

I've never had to readjust the edge doing it like this; I do of course test by pushing or

with a test tone. It is really fairly easy, the glue does sometimes start to set before I

finish putting it down - I just add a bit more as it seems to also get soaked into the

foam.

I have a few drivers to do here, and if M_Sound will send a sample set I'll test them for

Fs, it would be nice to verify another source. Just took a look on ebay, his prices are

high and he includes many things that I don't need, especially when doing more than one

pair of speakers without dust caps. He should offer a foam only option at a better

price, IMO.

[JKent]

4I have a few drivers to do here, and if M_Sound will send a sample set I'll test them for

Fs, it would be nice to verify another source. Just took a look on ebay, his prices are

high and he includes many things that I don't need, especially when doing more than one

pair of speakers without dust caps. He should offer a foam only option at a better

price, IMO.

OTOH, I looked at the RSSound foams. They look inexpensive at first but when you realize that price is for just ONE surround... Do the math. If you pay for 2 RSSond foams + S/H the price is 17.50. And RS Sound has a $20 minimum order. An MSound KIT, which includes EVERYTHING--foams, dust caps, shims, glue, even alcohol wipes, cotton swabs and sandpaper (AND S/H) is $26.20! I don't think that price is high and he provides lots of support. I'm an M Sound fan

Thanks again for the advice & guidance.

Kent

[Pete B]

OTOH, I looked at the RSSound foams. They look inexpensive at first but when you realize that price is for just ONE surround... Do the math. If you pay for 2 RSSond foams + S/H the price is 17.50. And RS Sound has a $20 minimum order. An MSound KIT, which includes EVERYTHING--foams, dust caps, shims, glue, even alcohol wipes, cotton swabs and sandpaper (AND S/H) is $26.20! I don't think that price is high and he provides lots of support. I'm an M Sound fan

Thanks again for the advice & guidance.

Kent

I didn't recall that the shipping was so high, both seem to be however I purchased 3 or 4 pairs last time with only a small increase in shipping.

[Pete B]

I and others can't seem to find RSSOUND so it is a moot point by now.

How did these turn out?

[JKent]

I and others can't seem to find RSSOUND so it is a moot point by now.

How did these turn out?

Hi Pete

A little behind. I have several KLH radios in varying stages of restoration, so the OLAs are on the back burner for now. Also--I'm currently in Key West, away from all my classic hi-fi stuff. Life is tough

Kent